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PubMed2004

Assessing macular pigment from SLO images.

PURPOSE: To assess the spectral characteristics and spatial distribution of macular pigment by comparing relative retinal reflectance at four different wavelengths. METHODS: A Rodenstock scanning laser opththalmoscope (SLO) with four spectral beams, 488, 544, 633 and 780 nm, was used to obtain images of the normal macula from five eyes of three normal subjects. The relative spectral reflectance was determined along a horizontal path extending from nasal to temporal retina through the fovea for each image. A comparison of this data provided an indication of the relative density and the actual spatial extent of macular pigmentation. RESULTS: There is an area of hyper-pigmentation obtained from averaging the data from all five eyes that extends from about 6 deg symmetrically into nasal and temporal macula surrounding a small zone of greater hyper-pigmentation that extends about 3 deg on each side of the fovea. The smaller central zone has a relatively high absorption for blue light and is considered to represent macular pigment. The larger less hyper-pigmented zone is considered to represent melanin in the retinal pigment epithelium. CONCLUSION: The circularly symmetrical hyper-pigmented central macula including the yellow macular pigment can be assessed by comparing different spectral images obtained from an SLO.

Adult↗
PubMed1981

Scanning and transmission electron microscopic studies of two cases of pigment dispersion syndrome.

We examined four eyes obtained post mortem from two patients who had increased intraocular pressure, normal visual fields, and pigment dispersion syndrome. Gross examination, light microscopy, scanning electron microscopy, and transmission electron microscopy disclosed elongated regions on the posterior iris surface of all the eyes. The cell membrane of the iris pigment epithelium was disrupted and there was extrusion of pigment granules at these locations. These areas of iris had a radial distribution (paralleling the course of the packets of zonular fibers) and corresponded to the peripheral iris transillumination defects. Pigment was dispersed in the anterior segment and on the pars plana. In the trabecular meshwork the pigment was free, within macrophages, and within endothelial cells. We observed giant vacuoles in the endothelium of Schlemm's canal. These findings suggested that friction between the zonular fibers and peripheral iris led to focal disruption of iris pigment epithelium and release of pigment granules. The increased pigment within the trabecular meshwork and Schlemm's canal may indicate that the glaucoma sometimes associated with pigment dispersion is caused by pigmentary obstruction, although congenital imperfections of the outflow channels may also be a factor

Aged↗
PubMed1984

Species differences in the hepatic formation of green pigments following the administration of norethindrone.

Metabolic activation of the ethynyl substituent of the contraceptive steroid norethindrone to cause the loss of hepatic cytochrome P-450 and the formation of green pigments has been compared in vivo and in vitro in rat, hamster, guinea pig, rabbit, mouse and hen and with marmoset and human liver microsomal preparations in vitro. In vivo green pigment accumulation in the liver 4 hr after the administration of norethindrone (100 mg/kg, i.p.) varied 60-fold between species. Male rat was the most active in this respect, the hen was the least active. The accumulation of green pigments in female rats was 27% that of male animals. This sex-dependent difference was not seen in male and female mice. Cytochrome P-450 destruction in vivo was also greatest in the male rat given norethindrone, whereas no loss was detected in the hen. In other species, however, the correlation between green pigment accumulation and cytochrome P-450 destruction was not particularly good. When liver microsomes were incubated with norethindrone and an NADPH generating system in vitro, the ranking order between species with respect to the initial rates of green pigment formation was similar to that based on the hepatic accumulation of these compounds found in vivo. Human liver microsomes showed initial rates of green pigment formation which were only 2% of that seen in the male rat. No destruction of human microsomal cytochrome P-450 caused by norethindrone could be detected. The HPLC elution profile of the green pigments produced in the liver following the administration of norethindrone differed between species. Hepatic microsomal preparations in contrast, at least with short incubation times, formed only one green pigment. Results suggest that further metabolism of either norethindrone or the green pigment, involving a cytosolic factor(s), results in the varied HPLC patterns seen in vivo.

Animals↗
PubMed1986

Destruction of cytochrome P-450 and formation of green pigments by contraceptive steroids in rat hepatocyte suspensions.

The contraceptive steroid norethindrone caused a rapid time and dose-dependent loss of cytochrome P-450 from rat hepatocytes in suspension cultures. Up to 30% of this cytochrome was lost in the first 5 min of incubation; longer incubations resulted in little further loss even though not all the steroid was metabolised and the cells remained viable. Such cultures were used to investigate the formation of N-alkylated porphyrins (green pigments) which could be extracted from cell incubation mixtures following exposure to norethindrone and separation by HPLC or TLC. The number of N-alkylated porphyrins formed was dependent both on the time of incubation and the concentration of steroid. After 1 min, 1 major green pigment (GP1) was resolved using either high (0.3 mM) or low (0.03 mM) norethindrone concentrations. With longer incubation times (60 min), at high steroid concentrations, only one additional polar adduct (GP2) was formed. At lower steroid levels, 3 more polar components (GP2, 3 and 4) were seen. As judged by HPLC or TLC, GP1 corresponds to the pigment formed in microsomal preparations incubated with norethindrone in vitro, while GP2, 3 and 4 correspond to the pigments extracted from the livers of rats administered this steroid in vivo. Pretreatment of rats with either phenobarbitone or 3-methylcholanthrene induced cytochrome P-450s. Relative to controls, phenobarbitone pretreatment also resulted in a greater accumulation of green pigments in hepatocytes incubated with norethindrone, the more polar forms of green pigments (GP3 and 4), showing a disproportionate increase in concentration. The mixed function oxidase inhibitor SKF 525-A or high concentrations of steroid not containing an ethynyl function, e.g. norethandrolone, when added to cell cultures containing norethindrone, preferentially inhibited the formation of GP3 and 4. When purified green pigments were added to cell incubation mixtures in the absence of norethindrone, preferentially inhibited the formation of GP3 and 4. When purified green pigments were added to cell incubation mixtures in the absence of norethindrone, no interconversion of one form to another could be demonstrated. The results suggest that the more polar norethindrone-protoporphyrin IX adducts (GP2, 3 and 4) arise as a result of metabolic modification of norethindrone rather than the protoporphyrin IX moiety, either prior to or after activation of the ethynyl function. The formation of several green pigment components in hepatocyte suspensions was not unique to norethindrone but occurred with a number of other 17-ethynyl-substituted steroids.

Animals↗
PubMed1992

Transdifferentiation of chicken retinal pigmented epithelial cells in serum-free culture.

A serum-free culture of chicken retinal pigmented epithelial cells has been established in order to analyse how cell-substrate interactions or environmental factors affect the process of transdifferentiation into lens cells from pigmented epithelial cells. The serum-free culture medium for chicken pigmented epithelial cells was Eagle's minimum essential medium, supplemented with chicken transferrin, soybean trypsin inhibitor and bovine insulin. Pigmented epithelial cells were able to survive and grow in the medium for longer than 2 weeks. Collagen did not promote initial cell attachment, but this material effectively supports pigmented epithelial cells to organize monolayer structure characteristics to pigmented epithelium in situ in comparison with the plastic substrate of culture dishes. The process of lens transdifferentiation of chicken pigmented epithelial cells in serum-free conditions was also enhanced with the aid of phenylthiourea and testicular hyaluronidase, which had already been known to promote the transdifferentiation of pigmented epithelial cells in the serum-supplemented condition. Typical lentoid bodies were developed after about 2 weeks of serum-free culture. Thus, we can clearly demonstrate that the chicken embryonic pigmented epithelial cells do not always require a full set of serum factors for their transdifferentiation to lens cells in vitro.

Animals↗
PubMed1986

Molecular biology of the visual pigments.

With the identification and structural characterization of several visual pigments has come a new era of investigation. The above comparisons of amino acids sequences predict specific functional domains that may be tested to tell us how visual pigments function to absorb light and transform this "signal" to trigger a neural response. The details of how rod and cone pigments differ are now known for human pigments. The striking similarities between vertebrate and invertebrate pigments are remarkable for pigments that have been subject to divergence for over 500 million years. There are yet challenges ahead of us. The true tertiary structure of visual pigments must be obtained from a 3-dimensional crystal structure. The predictions for functional domains of interaction with the GTP binding protein must be confirmed or redefined. A rigorous definition of the chromophore environment and the properties that control the wavelength of absorption of 11-cis retinal chromophore are certainly still on the drawing boards. Specific genetic alteration through in vitro mutagenesis promises much insight, but the technology for expressing these membrane proteins in functional form has yet to be achieved. We may expect, however, these problems will be addressed and in the next few years facts should replace what are now speculations. Finally, it is a delightful observation that nature has capitalized on a general biochemical mechanism for control of second messengers in the cytoplasm of cells. Protein structural data deduced from genetic information now document the hypothesis that the structure and function of receptors for the catecholamines and that of visual pigments are similar. The receptors for serotonin, leukotrienes, prostaglandins, histamine and acetylcholine (muscarinic) are expected to belong to this same family. The lessons learned about visual pigments can be applied broadly to a general set of membrane receptors.

Amino Acid Sequence↗
PubMed2004

Pigment cell lineage-specific expression activity of the ascidian tyrosinase-related gene.

Solitary ascidian tadpole larvae develop two types of black pigment cells in the major sensory organs of the brain. Such pigment cells have been demonstrated to express the melanogenic genes, tyrosinase and Tyrp/TRP (tyrosinase-related protein). To understand the genetic and developmental mechanisms underlying the differentiation of chordate pigment cells, we examined the function of the promoter region of Tyrp/TRP gene, an ascidian (Halocynthia roretzi) tyrosinase family gene. The expression of the gene in pigment cell lineage starts at the early-mid gastrula stages. To identify the transcriptional regulatory region of the gene allowing cell-type-specific expression, a deletion series of the HrTyrp 5' flanking region fused to a lacZ reporter gene was constructed and microinjected into ascidian fertilized eggs. The region of 73 bp in HrTyrp was identified as sufficient for expression in pigment cell-precursors of tailbud stage embryos. It is noteworthy that there is no M-box element highly conserved in the promoters for vertebrate tyrosinase family genes such as tyrosinase, Tyrp1/TRP-1 and Tyrp2/TRP-2 (Dct). Although the regulatory system of ascidian pigment-cell development is likely to contain most factors critical to vertebrate pigment-cell development, there might be critical differences in the mode of regulation, such as the developmental timing of interactions of factors, proteins and genes, involved in pigment cell differentiation and pigmentation.

5' Flanking Region↗
PubMed2005

Selected pigmented fundus lesions of children.

BACKGROUND: Ocular cells that accumulate melanin pigment are derived from 1 of 2 sources, the optic vesicle or the neural crest. Migration and distribution of pigment containing cells may go awry during fetal development or these cells may be altered before or after birth either by local or systemic stimuli. Specific recognition patterns of pigment distribution often exist and may relate directly to a single disease process. METHODS: Records of pediatric patients with disorders of pigment distribution in the ocular fundi who had been examined by the author were reviewed. RESULTS: Five disorders with recognizable patterns of retinal pigment epithelium (optic vesicle derivation) disturbance (congenital hypertrophy of the retinal pigment epithelium, Gardner syndrome, chronic granulomatous disease, preserved para-arteriole retinal pigment epithelium in (autosomal-recessive) retinitis pigmentosa, and combined hamartoma of the retina and retinal pigment epithelium), and 5 disorders of cells originating from the neural crest (choroidal nevi, choroidal melanoma, melanocytoma, ocular melanosis, and oculodermal melanosis), were selected for illustration and discussion. CONCLUSIONS: These arbitrarily selected groups of disorders affect or involve patterns of pigment deposition in the ocular fundus. These patterns are recognizable and distinguishable one from another but have different implications for treatment and follow-up. Progress in recognizing distinguishing characteristics, diagnostic implications, understanding, and treatment of these disorders during the past 40 years is compared and contrasted between the 2 groups.

Adolescent↗
PubMed2004

The Tomita collection of medaka pigmentation mutants as a resource for understanding neural crest cell development.

All body pigment cells in vertebrates are derived from the neural crest. In fish the neural crest can generate up to six different types of pigment cells, as well as various non-pigmented derivatives. In mouse and zebrafish, extensive collections of pigmentation mutants have enabled dissection of many aspects of pigment cell development, including fate specification, survival, proliferation and differentiation. A collection of spontaneous mutations collected from wild medaka (Oryzias latipes) populations and maintained at Nagoya University includes more than 40 pigmentation mutations. The descriptions of their adult phenotypes have been previously published by Tomita and colleagues (summarised in Medaka (Killifish) Biology and Strains, 1975), but the embryonic phenotypes have not been systematically described. Here we examine these embryonic phenotypes, paying particular attention to the likely defect in pigment cell development in each, and comparing the spectrum of defects to those in the zebrafish and mouse collections. Many phenotypes parallel those of identified zebrafish mutants, although pigment cell death phenotypes are largely absent, presumably due to the different selective pressures under which the mutants were isolated. We have identified mutant phenotypes that may represent the Mitf/Kit pathway of melanophore specification and survival. We use in situ hybridisation with available markers to confirm a key prediction of this hypothesis. We also highlight a set of novel phenotypes not seen in the zebrafish collection. These mutants will be a valuable resource for pigment cell and neural crest studies and will strongly complement the mutant collections in other vertebrates.

Animals↗
PubMed2001

Pigment epithelium-derived factor in the vitreous is low in diabetic retinopathy and high in rhegmatogenous retinal detachment.

PURPOSE: To report the levels of pigment epithelium-derived factor in the vitreous of patients with diabetic retinopathy, rhegmatogenous retinal detachment, and idiopathic macular hole. METHODS: Using enzyme-linked immunosorbent assay, we measured the levels of pigment epithelium-derived factor in the vitreous of 34 eyes of 33 patients who underwent vitrectomy for the treatment of diabetic retinopathy (17 eyes of 16 patients), rhegmatogenous retinal detachment (10 eyes), and idiopathic macular hole (seven eyes). RESULTS: The vitreal concentration of pigment epithelium-derived factor was 1.15 +/- 0.23 microg/ml (mean +/- standard error) in eyes with diabetic retinopathy, 3.28 +/- 0.69 microg/ml in rhegmatogenous retinal detachment, and 1.71 +/- 0.39 microg/ml in idiopathic macular hole. The pigment epithelium-derived factor level in rhegmatogenous retinal detachment was significantly higher than that in diabetic retinopathy (P =.0008) and idiopathic macular hole (P =.034). For eyes with diabetic retinopathy, the pigment epithelium-derived factor level was 0.88 +/- 0.21 microg/ml in proliferative diabetic retinopathy and 2.43 +/- 0.37 microg/ml in nonproliferative diabetic retinopathy (P =.0083). Additionally, the pigment epithelium-derived factor level in active diabetic retinopathy (0.70 +/- 0.22 microg/ml) was significantly lower than the level in inactive diabetic retinopathy (1.79 +/- 0.35 microg/ml; P =.018). CONCLUSIONS: These results suggest that pigment epithelium-derived factor inhibits angiogenesis and that lower levels of pigment epithelium-derived factor may be related to the angiogenesis in diabetic retinopathy and result in active proliferative diabetic retinopathy. The results also suggest that higher levels of pigment epithelium-derived factor in the eyes with rhegmatogenous retinal detachment may act as a neuroprotective agent for the detached retina.

Adult↗
PubMed1997

Indocyanine green videoangiography after acute retinal pigment epithelial tears in age-related macular degeneration.

PURPOSE: To determine the features of combined fluorescein and indocyanine green videoangiography after acute retinal pigment epithelial tears associated with age-related macular degeneration. METHODS: We performed combined fluorescein and indocyanine green videoangiography in three eyes of three patients 2 days to 2 months after the development of tears of the retinal pigment epithelium. RESULTS: The area of exposed choroid in a retinal pigment epithelial tear shows intense hyperfluorescence in fluorescein videoangiography; in contrast, this area demonstrates near-normal choroidal fluorescence on an indocyanine green videoangiogram. The folded and retracted flap of retinal pigment epithelium in a retinal pigment epithelial tear discloses marked hypofluorescence on the fluorescein videoangiogram; in contrast, this flap of retinal pigment epithelium displays varying degrees of hyperfluorescence on the indocyanine green videoangiogram. CONCLUSIONS: The angiographic differences between fluorescein and indocyanine green result from the distinct biophysical properties of these two dyes as well as from the differential penetration of their fluorescence through such pigmented structures as retinal pigment epithelium. Compared with fluorescein videoangiography, indocyanine green videoangiography allows better visualization of choroidal neovascular membranes within the rolled-up and retracted flap of the retinal pigment epithelial tear.

Acute Disease↗
PubMed1989

Timing in the regulation of neural crest cell migration: retarded "maturation" of regional extracellular matrix inhibits pigment cell migration in embryos of the white axolotl mutant.

In larvae of the white axolotl mutant (Ambystoma mexicanum), contrary to normal dark ones, trunk pigmentation is restricted because the epidermis is unable to support subepidermal migration of pigment cells from the neural crest (NC). This study examines whether the subepidermal extracellular matrix (ECM) is the defective component which prevents pigment cell migration in the white embryo. We transplanted subepidermal ECM, adsorbed in vivo on membrane microcarriers, from and to white and dark embryos in various combinations. White embryos have demonstrated normal NC cell migration along the medioventral pathway, and in order to test the effects of medial ECM on subepidermal migration, this ECM was similarly transplanted. Carriers with ECM attached were inserted subepidermally in host embryos at a premigratory NC stage. Control carriers without ECM and carriers with subepidermal ECM from white donors did not affect NC cell migration in white or dark embryos. In contrast, subepidermal ECM from dark donors triggered NC cell migration in the subepidermal space of both white and dark hosts. Remarkably, subepidermal ECM from white donors which were older than those normally used also stimulated migration in embryos of both strains. Likewise, medial ECM from white donors elicited migration in white as well as dark hosts. Pigment cells occurred among those NC cells that were stimulated to migrate in response to contact with ECM on carriers. These results indicate that the subepidermal ECM of the white embryo is transiently defective as a substrate for pigment cell migration, implying that "maturation" of the ECM is retarded beyond the times during which pigment cells are able to respond. In contrast, the medial ECM of the white embryo appears to mature normally. These findings suggest that the effect of the d gene is expressed regionally through the subepidermal ECM during a limited period of development. Hence, the action of the d gene seems to retard ECM maturation, bringing it out of phase with the migratory capability of the pigment cells. We propose that such a shift in relative timing of the developmental phenomena involved inhibits pigment cell migration in embryos of the white axolotl mutant and, accordingly, that the restricted pigmentation of the mutant larva is generated through heterochrony.

Ambystoma mexicanum↗
PubMed1982

Frequency of black pigment in livers and spleens of coal workers: correlation with pulmonary pathology and occupational information.

Histologic sections of liver and spleen from 99 retired coal workers and nine non-coal workers were obtained at autopsy and scored for black pigment. Pigment was minimal in the non-coal workers, with the exception of one person with silicosis. Moderate or heavy pigment was seen in 10.4 per cent of liver sections and 19.5 per cent of spleen sections from coal workers. The extrapulmonary pigment was not associated with any pathologic tissue response. Information on pulmonary pathology and occupational exposure to dust was available for most workers. Highly significant positive correlation was found between the severity of pneumoconiosis and the black pigment score in both liver and spleen; the correlation between emphysema and pigment score was lower, but still significant for liver. Significant positive correlations were found between years spent underground, years of retirement, and age at death versus pigment scores. Significant negative correlation was found between smoking and pigment. The positive association of extrapulmonary pigment with age at death, years of underground mining, and severity of pneumoconiosis suggests that cumulative lifetime exposure to coal mine dust may be the most important factor in the release of dust into the general circulation.

Coal Mining↗
PubMed1999

Effects of lithium on pigmentation in the embryonic zebrafish (Brachydanio rerio).

Pigment cell precursors of the embryonic zebrafish give rise to melanophores, xanthophores and/or iridophores. Cell signaling mechanisms related to the development of pigmentation remain obscure. In order to examine the mechanisms involved in pigment cell signaling, we treated zebrafish embryos with various activators and inhibitors of signaling pathways. Among those chemicals tested, LiCl and LiCl/forskolin had a stimulatory effect on pigmentation, most notable in the melanophore population. We propose that the inositol phosphate (IP) pathway, is involved in pigment pattern formation in zebrafish through its involvement in the: (1) differentiation/proliferation of melanophores; (2) dispersion of melanosomes; and/or (3) synthesis/deposition of melanin. To discern at what level pigmentation was being effected we: (1) counted the number of melanophores in control and experimental animals 5 days after treatment; (2) measured tyrosinase activity and melanin content; and (3) employed immunoblotting techniques with anti-tyrosine-related protein-2 and anti-melanocyte-specific gene-1 as melanophore-specific markers. Although gross pigmentation increased dramatically in LiCl- and LiCl/forskolin treated embryos, the effect on pigmentation was not due to an increase in the proliferation of melanophores, but was possibly through an increase in melanin synthesis and/or deposition. Collectively, results from these studies suggest the involvement of an IP-signaling pathway in the stimulation of pigmentation in embryonic zebrafish through the synthesis/deposition of melanin within the neural crest-derived melanophores.

Animals↗
PubMedDate not supplied

Pathogenesis of pigment gallstones in Western societies: the central role of bacteria.

Bacteria are traditionally accorded a greater role in pigment gallstone formation in Eastern populations. Stone color is thought to predict the presence of bacteria; that is, black stones (Western predominant) are supposedly sterile and brown stones (Eastern predominant) contain bacteria. We previously reported that, regardless of appearance, most pigment gallstones contain bacteria. This study examined, in a large Western population (370 patients), the incidence, appearance, and chemical composition of pigment stones, and the characteristics of gallstone bacteria. One hundred eighty-six pigment stones were obtained aseptically. Bacteria were detected by means of scanning electron microscopy and gallstone culture. Chemical composition was determined by infrared spectroscopy. Bacteria were tested for slime and beta-glucuronidase production. Seventy-three percent of pigment stones contained bacteria. Choledocholithiasis was associated with gallstone bacteria. Ca-bilirubinate was present in all pigment stones. Ca-palmitate was characteristic of infected stones, and more than 75% Ca-carbonate was characteristic of sterile stones. Neither chemical composition nor stone appearance predicted the presence of bacteria. Ninety-five percent and 67% of infected pigment stones contained bacteria that produced slime and beta-glucuronidase, respectively. Most pigment stones contained bacteria that produced beta-glucuronidase, slime, and phospholipase, factors that facilitate stone formation. Thus bacteria have a major role in Western pigment gallstone formation. Furthermore, gallstone color did not predict composition or bacterial presence.

Adolescent↗
PubMedDate not supplied

Visual pigments in the sea lamprey, Petromyzon marinus.

We present microspectrophotometric evidence for the existence of two distinct visual pigments residing in two different morphological types of photoreceptor of the sea lamprey. In the upstream migrant Petromyzon marinus, the pigment found in short receptors has a wavelength of peak absorbance (lambda max) of 525 nm, whereas the pigment located in long receptors has a lambda max of 600 nm. Although the former appears to be pure porphyropsin, the latter is akin to visual pigments found in the red-absorbing cones of amphibian and teleost retinae. The kinship is more than superficial pertaining to lambda max, however, because the long receptor pigment, like the others, shows the typical sensitivity to the anionic milieu. Lampreys belong to the class Cyclostomata, which now becomes the sixth phylogenetic class of vertebrates with anion-sensitive as well as anion-insensitive visual pigments. This finding strengthens the hypothesis that sensitivity to anions is an integral property of all long-wavelength-absorbing vertebrate pigments and that these pigments form a distinct group in which an external Cl- ion is utilized in tuning the lambda max of the alpha-band absorbance to its native maximum value. The presence of an anion-sensitive and an anion-insensitive pigment in a retina implies the expression of two distinct opsin genes. We infer this from several examples of correlation between anion sensitivity and opsin sequence groupings. Moreover, the presence of two distinct opsin genes expressed throughout six vertebrate classes implies their existence in a common ancestor to all.

Absorption↗
PubMedDate not supplied

Cone visual pigments of the Australian marsupials, the stripe-faced and fat-tailed dunnarts: sequence and inferred spectral properties.

Studies of color vision in marsupial mammals have been very limited. Two photoreceptor genes have been characterized from the tammar wallaby, but a third cone pigment was suggested by microspectrophotometric measurements on cone photoreceptors in two other species, including the fat-tailed dunnart, Sminthopsis crassicaudata. To determine the sequence and infer absorption maxima of the cone photoreceptor pigments of S. crassicaudata and the related stripe-faced dunnart (Sminthopsis macroura), we have used evolutionarily conserved sequences of the cone pigments of other species, including the tammar wallaby, to design primers to amplify the S. macroura and S. crassicaudata pigment sequences by the polymerase chain reaction (PCR) using genomic DNA or retinal cDNA as a template. These primers will be useful for amplifying cone opsin coding sequences from a variety of vertebrates. Amplified products were directly sequenced to determine gene structure and coding sequences. The inferred amino acid sequences of the cone visual pigments indicated that both species have middle-wave-sensitive (MWS) pigments with a predicted absorption maximum (lambda(max)) at 530 nm, and ultraviolet-sensitive (UVS) pigments with a predicted lambda(max) at 360 nm. The MWS pigments of the two species differ by two, and UVS by three amino acid positions. No evidence was obtained for a third cone pigment in either species.

Amino Acid Sequence↗
PubMed2005

A dark and constitutively active mutant of the tiger salamander UV pigment.

A triple mutant (F86L/T93P/S118T; bovine rhodopsin numbering) of the tiger salamander UV cone pigment appears to be trapped in an open conformation that is metarhodopsin-II-like. The pigment is able to activate transducin in the dark, and the ligand-free apoprotein is also able to activate transducin constitutively. The pigment permits protons and chloride ions from solution access to the active site as it displays a pH- and NaCl-dependent absorption spectrum not observed with the wild-type pigment. However, the wild-type properties of light-dependent activity and a pH-independent absorption spectrum are recovered upon reconstitution of the triple mutant with 11-cis-9-demethyl retinal. These results suggest that binding the native chromophore cannot deactivate the protein because of steric interactions between the protein, possibly residue 118, and the 9-methyl group of the chromophore. Furthermore, the absorption spectrum of the 9-demethyl retinal regenerated pigment exhibits a band broader and with lower extinction at the absorption maximum than either the human blue or salamander UV wild-type pigments generated with the same retinal analogue. The broad spectrum appears to be comprised of two or more species and can be well-fit by a sum of scaled spectra of the two wild-type pigments. Binding the chromophore appears to trap the pigment in two or more conformations. The triple mutant reported here represents the first example of a dark-active cone pigment and constitutively active cone opsin.

Ambystoma↗